Lithium ion battery electrolyte and application thereof

Abstract

The application provides a lithium ion battery electrolyte and application thereof, and the electrolyte comprises: a nonaqueous solvent; a lithium salt; and an additive, wherein the additive comprises a first additive and a second additive; the first additive is selected from compounds represented by any one of formulas (I) to (III); and the second additive comprises lithium difluorophosphate dioxalate; wherein R1 to R7 are substituents with 1 to 3 carbon atoms, 0 to 4 unsaturation degrees and 0 to 3 heteroatom numbers; R8 is a cyclic substituent with 0 to 4 unsaturation degrees and 0 to 5 heteroatom numbers; when the unsaturation degree of R8 is 0, R9 is a vinyl group, a propenyl group, a butenyl group, a 1,3-butadienyl group, an ethynyl group or a propynyl group; when the unsaturation degree of R8 is 1 to 4, the R9 substituent is absent; the heteroatom is selected from at least one of nitrogen, sulfur, phosphorus, chlorine, fluorine and oxygen; and n is 0 to 2. The lithium ion battery electrolyte and application thereof simultaneously consider the low-temperature performance, high-temperature performance and gas production performance of the lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of power batteries, and in particular to a lithium-ion battery electrolyte and applications thereof. Background Art

[0002] As a key component of lithium-ion batteries, the performance and safety of lithium-ion battery electrolytes have a crucial impact on the performance and safety of the entire battery system. Therefore, continuously optimizing the performance and safety of electrolytes is an important direction for the continued development of the lithium-ion battery field.

[0003] Due to the high melting point and high viscosity of traditional lithium-ion battery electrolytes, the reaction rate of the electrolyte slows significantly when the ambient temperature drops, severely limiting the performance of lithium-ion batteries at low temperatures. Although some electrolytes with better kinetics can improve the low-temperature performance of lithium-ion batteries to a certain extent, these electrolytes often cannot maintain their high-temperature performance while pursuing low-temperature performance. This makes it difficult to fully balance the performance of batteries in high and low temperature environments, limiting their scope of application. Summary of the Invention

[0004] The present invention proposes a lithium-ion battery electrolyte and its application. Through the lithium-ion battery electrolyte and its application provided by the present invention, the quality of the positive electrode-electrolyte interface and the negative electrode-electrolyte interface are improved at the same time, which can effectively reduce the battery impedance and improve the low-temperature performance of the battery, while taking into account the high-temperature performance and gas production performance.

[0005] To solve the above technical problems, the present invention provides a lithium-ion battery electrolyte comprising at least the following components:

[0006] non-aqueous solvents;

[0007] lithium salts; and

[0008] Additives, the additives include a first additive and a second additive, the first additive is selected from a compound represented by any one of formula (I) to formula (III), and the second additive includes lithium difluorobis(oxaloyl)phosphate:

[0009] Formula (I), Formula (II) or

[0010] Formula (III);

[0011] Wherein, R1, R2, R3 and R4 are substituents with 1-3 carbon atoms, 0-4 unsaturations and 0-3 heteroatoms respectively; R5, R6 and R7 are substituents with 1-3 carbon atoms, 0-4 unsaturations and 0-3 heteroatoms respectively; R8 is a cyclic substituent with 0-4 unsaturations and 0-5 heteroatoms; when the unsaturation of R8 is 0, R9 is ethenyl, propenyl, butenyl, 1,3-butadienyl, ethynyl or propynyl; when the unsaturation of R8 is 1-4, the R9 substituent does not exist; the heteroatoms are selected from at least one of nitrogen, sulfur, phosphorus, chlorine, fluorine or oxygen, and n is 0-2.

[0012] In one embodiment of the present invention, R1, R2, R3 and R4 are respectively alkyl, alkenyl, alkynyl, carbonyl, ester or amino; R5, R6 and R7 are respectively alkyl, alkenyl, alkynyl or amino.

[0013] In one embodiment of the present invention, the content of the first additive in the electrolyte is 0.1 wt%-3 wt%, and the content of the second additive in the electrolyte is 0.1 wt%-3 wt%.

[0014] In one embodiment of the present invention, the content of the first additive in the electrolyte is 0.5 wt %-1 wt %, and the content of the second additive in the electrolyte is 0.5 wt %-1 wt %.

[0015] In one embodiment of the present invention, the first additive is selected from at least one of the following compounds:

[0016] Compound 1 or Compound 2.

[0017] In one embodiment of the present invention, the non-aqueous solvent is selected from at least one of ethylene carbonate, polycarbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, propyl propionate, ethyl propionate or ethyl acetate, and the content of the non-aqueous solvent in the electrolyte is 70wt%-85wt%.

[0018] In one embodiment of the present invention, the lithium salt is selected from one or a combination of at least two of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium methanesulfonate and lithium trifluoromethylsulfonate, and the content of the lithium salt in the electrolyte is 12 wt%-16 wt%.

[0019] The present invention also provides a lithium ion battery comprising the lithium ion battery electrolyte described above.

[0020] In one embodiment of the present invention, the positive electrode active material of the lithium ion battery includes Li x [Niy Co z Mn t M (1-y-z-t) ]O 2-δ or at least one of lithium iron phosphate, wherein M is at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W or Zn, 0.9 < x < 1.1, 0 < y < 1.0, 0 < z < 1, 0 < t < 1, 0 ≤ δ ≤ 0.1; the negative active material of the lithium battery comprises at least one of graphite, silicon-oxygen material or silicon-carbon material.

[0021] The present application also provides an electrochemical device comprising the lithium ion battery described above.

[0022] In summary, the present application proposes a lithium ion battery electrolyte and its application. By using the first additive and the second additive together, the solubility of the second additive can be enhanced by intermolecular interaction. The unsaturated bond in the first additive can capture F- generated by the breaking of P-F bond to form C-F covalent bond, further addition reaction of the chain occurs on the positive electrode side, improving the stability of the positive electrode interface, reducing the decomposition of non-aqueous solvent gas, and protecting the transition metal ions in the positive electrode from HF corrosion. The combination of the first additive and the second additive can fully exert the advantages of both, improve the quality of the positive electrode-electrolyte interface and the negative electrode-electrolyte interface, effectively reduce the battery impedance, improve the low temperature performance of the battery, and at the same time, take into account the high temperature performance and gas production performance. DETAILED DESCRIPTION

[0023] The embodiments of the present application will be described in detail below with specific examples. Those skilled in the art can easily understand other advantages and effects of the present application from the disclosure. The present application can also be implemented or applied in different specific embodiments, and various modifications or changes can be made to the details in the specification without departing from the spirit of the present application.

[0024] It should be understood that the present application can be implemented in different forms, and should not be interpreted as being limited to the examples presented herein. On the contrary, these examples are provided to make the disclosure complete and complete, and to fully convey the scope of the present application to those skilled in the art.

[0025] The technical solutions of the present application will be further described below in combination with examples. Obviously, the described examples are only a part of the examples of the present application, not all examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0026] The present invention proposes a lithium-ion battery, which is, for example, a primary battery or a secondary battery, and the secondary battery is, for example, a soft-pack battery, a square-shell battery or a cylindrical battery. The present invention does not specifically limit the type of lithium-ion battery. Here, a cylindrical battery is taken as an example to illustrate the specific implementation of the present invention. In one embodiment of the present invention, the lithium-ion battery includes a shell and a bare cell arranged in the shell. The bare cell includes a positive electrode sheet, a diaphragm and a negative electrode sheet. The positive electrode sheet, the diaphragm and the negative electrode sheet are stacked in sequence to ensure that a diaphragm is provided between any positive electrode sheet and any negative electrode sheet. A multi-layer laminate is obtained by winding and is loaded into a battery shell as a bare cell. Finally, the electrolyte is injected into the shell once or multiple times so that the bare cell is completely immersed in the electrolyte.

[0027] In one embodiment of the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector. The positive electrode current collector is, for example, a foil formed by surface treatment of nickel, titanium, aluminum, silver, stainless steel or carbon. In addition to foil, the positive electrode current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam or non-woven fabric. The thickness of the positive electrode current collector is, for example, 8μm-15μm. In this embodiment, the positive electrode current collector is, for example, aluminum foil, and the thickness of the aluminum foil is, for example, 13μm.

[0028] In one embodiment of the present invention, the positive electrode active material layer includes a positive electrode active material, a binder, and a conductive agent. The positive electrode active material includes at least one of a ternary material and lithium iron phosphate (LiFePO4). The ternary material is, for example, Li x [Ni y Co z Mn t M (1-y-z-t) ]O 2-δ, wherein M is selected from at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W or Zn, etc., 0.9 <x<1.1,0<y<1.0,0<z<1.0,0<t<1.0,0≤δ≤0.1,以提高锂离子电池的能量密度和循环寿命。粘接剂例如选自聚偏二氟乙烯(Polyvinylidene Fluoride,PVDF)、聚环氧乙烷(Poly(ethylene oxide),PEO)、聚酰胺(Polyamide,PA)、聚丙烯腈(Polyacrylonitrile,PAN)、聚丙烯酸酯(Polyacrylate)、聚乙烯醚(Polyvinylether)、聚甲基丙烯酸甲酯(Polymethyl Methacrylate,PMMA)、乙烯-丙烯-双烯三元共聚物(EPDM)、聚六氟丙烯(Polyhexafluoropropylene)或丁苯橡胶(Polymerized Styrene ButadieneRubber,SBR)等中的任意一种或多种。导电剂例如选自导电炭黑(Super P)、乙炔黑、碳纳米管和石墨烯等中任意一种或多种。

[0029] In one embodiment of the present invention, the positive electrode active material is, for example, LiNi 0.9 Mn 0.05 Co 0.05 O2, the binder is selected from polyvinylidene fluoride, and the conductive agent is selected from conductive carbon black. After mixing the positive electrode active material, the conductive agent and the binder, for example, in a mass ratio of (90-98): (1-5): (1-5), an organic solvent is added and stirred under the action of a vacuum mixer until the system is uniform to obtain a positive electrode slurry. Among them, the organic solvent is selected from N-methylpyrrolidone (NMP). The positive electrode slurry is evenly coated on an aluminum foil, and then transferred to an oven for drying after drying at room temperature. The positive electrode sheet is obtained through processes such as cold pressing and slitting. In other embodiments, the positive electrode sheet can also be obtained by any other method of forming the positive electrode sheet.

[0030] In one embodiment of the present invention, the negative electrode plate includes, for example, a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode current collector is, for example, selected from a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foam copper current collector, or a stainless steel current collector, and has a thickness of, for example, 8 μm to 15 μm. In this embodiment, the negative electrode current collector is, for example, copper foil, and the thickness of the copper foil is, for example, 13 μm.

[0031] In one embodiment of the present invention, the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, and a thickener. The negative electrode active material is a compound capable of intercalating and deintercalating lithium ions. In one embodiment of the present invention, the negative electrode active material includes, for example, graphite, silicon oxide (SiO x , 0 <x<2)或硅碳材料中的至少一种。粘接剂例如选自聚偏二氟乙烯、聚环氧乙烷、聚酰胺、聚丙烯、聚丙烯酸酯、聚乙烯醚、聚甲基丙烯酸甲酯、聚六氟丙烯或丁苯橡胶等中的任意一种或多种。增稠剂例如选择羧甲基纤维素钠(Carboxymethyl Cellulose Sodium,CMC-Na)等,导电剂例如选自导电炭黑、乙炔黑、科琴黑、碳纳米管和石墨烯等中任意一种或多种。

[0032] In one embodiment of the present invention, the negative electrode active material is selected from graphite and silicon-carbon material, and the mass ratio of silicon-carbon material to graphite is, for example, 2:98-10:90. The conductive agent is selected from conductive carbon black, the thickener is selected from sodium carboxymethyl cellulose, and the binder is selected from styrene-butadiene rubber. In one embodiment of the present invention, the negative electrode active material, conductive agent, binder, and thickener are mixed in a mass ratio of, for example, (90-96): (1-2): (1-3): (2-5), deionized water is added, and the mixture is mixed evenly in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is coated on copper foil, and then dried at room temperature and then transferred to an oven for drying. After cold pressing and slitting, a negative electrode sheet is obtained. In other embodiments, the negative electrode sheet can also be obtained by any other method of forming a negative electrode sheet.

[0033] In one embodiment of the present invention, the separator is, for example, a polyethylene (PE) film, a polypropylene (PP) film, a glass fiber film, or a composite film. The separator has a thickness of, for example, 9 μm to 15 μm. In one embodiment of the present invention, the separator is, for example, a polyethylene base film of 8 μm to 10 μm thick, and a nano-aluminum oxide coating having a thickness of 2 μm to 4 μm is applied to the base film to obtain the separator.

[0034] In one embodiment of the present invention, the lithium-ion battery also includes an electrolyte that is injected into and fills the entire internal space of the battery. The positive electrode, separator, and negative electrode are completely immersed in the electrolyte. The electrolyte plays a role in conducting ions, providing ion channels, and maintaining chemical stability. The various components in the electrolyte can be divided into non-aqueous solvents, lithium salts, and additives according to their functions and addition amounts. The non-aqueous solvent is used to dissolve the lithium salts and additives; the lithium salt is mainly used to provide lithium ions to form ion channels. In the entire electrochemical system of the battery, the directional movement of lithium ions and electrons generates electricity. The lithium salt has a significant impact on the energy density, power density, wide electrochemical window, cycle life, and safety performance of the lithium battery. Additives are substances added in small amounts to the electrolyte. There are many types and each plays a different role. For example, they can have different improvements on the high and low temperature performance, cycle performance, and film formation performance of the battery.

[0035] The present invention provides a lithium-ion battery electrolyte comprising at least a non-aqueous solvent, a lithium salt, and an additive, wherein the additive comprises a first additive and a second additive, and the first additive is a compound represented by any one of formulas (I) to (III):

[0036] Formula (I), Formula (II) or

[0037] Formula (III); wherein R1, R2, R3, and R4 are each a substituent having 1-3 carbon atoms, 0-4 degrees of unsaturation, and 0-3 heteroatoms. In one embodiment of the present invention, R1, R2, R3, and R4 are each a substituent such as an alkyl group, an alkenyl group, an alkynyl group, a carbonyl group, an ester group, or an amino group. R5, R6, and R7 are each a substituent having 1-3 carbon atoms, 0-4 degrees of unsaturation, and 0-3 heteroatoms. In one embodiment of the present invention, R5, R6, and R7 are each a substituent such as an alkyl group, an alkenyl group, an alkynyl group, or an amino group. R8 is a cyclic substituent having 0-4 degrees of unsaturation and 0-5 heteroatoms. When the unsaturation of R8 is 0, R9 is ethenyl, propenyl, butenyl, 1,3-butadienyl, ethynyl, or propynyl. When the unsaturation of R8 is 1-4, the R9 substituent is absent. The heteroatom included in formulas (I) to (III) is selected from at least one of nitrogen, sulfur, phosphorus, chlorine, fluorine, or oxygen, and n in formulas (I) to (II) is 0 to 2. The second additive includes lithium difluorodioxalatophosphate (LiODFP), which has the ability to form positive and negative electrode films, improve the quality of the cathode-electrolyte interphase (CEI) and the anode-electrolyte interface (SEI), and can effectively reduce battery impedance and enhance the low-temperature performance of the battery.

[0038] In one embodiment of the present invention, the first additive is selected from Compound 1 or At least one of compound 2, etc. Among them, since the first additive has an unsaturated bond, when the first additive and the second additive are used in combination, the solubility of the second additive LiODFP can be enhanced through intermolecular interaction. In addition, the unsaturated bond in the first additive can capture F- generated by the PF bond breakage, forming a CF covalent bond, further causing a chain addition reaction on the positive electrode side, improving the stability of the positive electrode interface, reducing the decomposition and gas production of the non-aqueous solvent, and protecting the transition metal ions in the positive electrode from HF corrosion. The combination of the first additive and the second additive can give full play to the advantages of both, improve the low-temperature performance of the battery, and take into account the high-temperature performance and gas production performance.

[0039] In an embodiment of the present application, the content of the first additive in the electrolyte is, for example, 0.1 wt% to 3 wt%, and for example, 0.5 wt% to 1 wt%. The content of the second additive in the electrolyte is, for example, 0.1 wt% to 3 wt%, and for example, 0.5 wt% to 1 wt%. If the content of the first additive is too low, the stability of the formed CEI film is poor, and the high-temperature storage and gas production performance is poor. If the content of the first additive is too high, the thickness of the CEI film is too thick, which is not conducive to the capacity of the battery. If the content of the second additive is too low, the high-temperature storage capacity recovery rate is large. If the content of the second additive is too high, the low-temperature performance of the lithium ion battery is improved, but the electrolyte gas production is increased, resulting in poor high-temperature storage performance and gas production performance. Therefore, by controlling the content of the first additive and the second additive, the high-temperature performance and low-temperature performance of the lithium ion battery are comprehensively improved, and the gas production is reduced.

[0040] In an embodiment of the present application, the lithium salt is, for example, at least one selected from lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethyl)sulfonylimide (LiTFSI), lithium methylsulfonate, and lithium trifluoromethylsulfonate (CF3SO3Li), and the content of the lithium salt in the electrolyte is, for example, 12 wt% to 16 wt%. The present application does not limit the type of lithium salt, and a single lithium salt or a mixed lithium salt can be used.

[0041] In an embodiment of the present application, the non-aqueous solvent is, for example, at least one selected from ethylene carbonate (EC), polycarbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), propyl phenyl acetate (PP), ethyl propionate (EP), and ethyl acetate (EA), and the content of the non-aqueous solvent in the electrolyte is, for example, 70 wt% to 85 wt%. In a specific embodiment of the present application, the non-aqueous solvent is, for example, a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0042] In one embodiment of the present invention, when preparing the electrolyte, the content of a stable gas such as nitrogen or argon in the glove box is 99.999%, the actual oxygen content in the glove box is less than or equal to 0.1 ppm, and the moisture content is less than or equal to 0.1 ppm. After uniformly mixing the non-aqueous solvent according to a mass ratio, a fully dried lithium salt is added to the non-aqueous solvent, and additives are added to prepare a non-aqueous electrolyte for a lithium-ion battery. The contents of the lithium salt and additives, excluding the non-aqueous solvent, are expressed in weight percentages based on the total weight of the electrolyte.

[0043] In one embodiment of the present invention, the aforementioned positive electrode sheet, separator, and negative electrode sheet are sequentially arranged, with the separator positioned between the positive and negative electrode sheets to provide isolation. The sheets are then wound or laminated to produce a bare cell. The bare cell is then placed in a housing, dried in a vacuum oven, injected with the electrolyte prepared herein, and sealed. The battery is then subjected to at least a resting, formation, and capacity separation step to produce a lithium-ion secondary battery.

[0044] Hereinafter, the present invention will be explained in more detail by citing examples, which should not be construed as limiting. Appropriate modifications may be made within the scope consistent with the gist of the present invention, all of which fall within the technical scope of the present invention.

[0045] Example 1

[0046] Preparation of the electrolyte: In an argon glove box with a moisture content of less than 0.1 ppm and an oxygen content of less than 0.1 ppm, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in a mass ratio of 3:5:2 to obtain a mixed solvent. Dry lithium hexafluorophosphate, compound 1, and lithium difluorobis(oxalate)phosphate were then added to the mixed solvent and mixed to obtain an electrolyte. The obtained electrolyte contained 12 wt% of the lithium salt, 0.5 wt% of the compound 1, and 0.1 wt% of the lithium difluorobis(oxalate)phosphate.

[0047] Preparation of positive electrode: LiNi 0.9 Mn 0.05 Co 0.05 O2, polyvinylidene fluoride, and conductive carbon black are mixed in a mass ratio of 98:1:1, then N-methylpyrrolidone is added. The mixture is stirred in a vacuum mixer until uniform, creating a positive electrode slurry. The slurry is evenly coated onto aluminum foil, air-dried at room temperature, and then oven-dried. The positive electrode sheets are then cold-pressed and slit.

[0048] Preparation of the negative electrode sheet: The negative electrode active material, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber are mixed in a mass ratio of 96:1:1:2. The negative electrode active material is a mixture of silicon-carbon material and graphite in a mass ratio of 5:95. Deionized water is added and mixed evenly in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is coated on copper foil, dried at room temperature, and then transferred to an oven for drying. After cold pressing and slitting, the negative electrode sheet is obtained.

[0049] Selection of diaphragm: 12μm polyethylene was selected as the diaphragm.

[0050] Battery Preparation: The positive electrode sheet, separator, and negative electrode sheet are wound sequentially, with the separator positioned between the positive and negative electrodes to provide insulation, resulting in a cylindrical bare cell. This cell is then placed in a circular casing, dried in a vacuum oven, and sealed with the electrolyte prepared above. This electrolyte is then formed to produce a lithium-ion secondary battery.

[0051] Example 2

[0052] The first additive is compound 1, the content of compound 1 is 0.5 wt %, the content of lithium difluorobis(oxaloyl)phosphate is 0.5 wt %, and the other steps are consistent with Example 1.

[0053] Example 3

[0054] The first additive is compound 1, the content of compound 1 is 0.5 wt %, the content of lithium difluorobis(oxaloyl)phosphate is 1 wt %, and the other steps are consistent with Example 1.

[0055] Example 4

[0056] The first additive is compound 1, the content of compound 1 is 0.5 wt %, the content of lithium difluorobis(oxaloyl)phosphate is 1.5 wt %, and the other steps are consistent with Example 1.

[0057] Example 5

[0058] The first additive is compound 1, the content of compound 1 is 0.5 wt %, the content of lithium difluorobis(oxaloyl)phosphate is 3 wt %, and the other steps are consistent with Example 1.

[0059] Example 6

[0060] The first additive is compound 1, the content of compound 1 is 0.1 wt %, the content of lithium difluorobis(oxaloyl)phosphate is 0.5 wt %, and the other steps are consistent with Example 1.

[0061] Example 7

[0062] The first additive is compound 1, the content of compound 1 is 1 wt %, the content of lithium difluorobis(oxaloyl)phosphate is 0.5 wt %, and the other steps are consistent with Example 1.

[0063] Example 8

[0064] The first additive is compound 1, the content of compound 1 is 1.5 wt %, the content of lithium difluorobis(oxaloyl)phosphate is 0.5 wt %, and the other steps are consistent with Example 1.

[0065] Example 9

[0066] The first additive is compound 1, the content of compound 1 is 3 wt %, the content of lithium difluorobis(oxaloyl)phosphate is 0.5 wt %, and the other steps are consistent with Example 1.

[0067] Example 10

[0068] The first additive is compound 2, the content of compound 2 is 0.5 wt %, the content of lithium difluorobis(oxaloyl)phosphate is 0.5 wt %, and the other steps are consistent with Example 1.

[0069] Comparative Example 1

[0070] Only the first additive was added. Compound 1 was selected as the first additive. The content of Compound 1 was 0.5 wt %. Other steps were the same as those in Example 1.

[0071] Comparative Example 2

[0072] The first additive is compound 1, the content of compound 1 is 0.5 wt %, the content of lithium difluorobis(oxaloyl)phosphate is 5 wt %, and the other steps are consistent with Example 1.

[0073] Comparative Example 3

[0074] Only lithium difluorobisoxalate phosphate was added, and the content of lithium difluorobisoxalate phosphate was 0.5 wt %. Other steps were the same as those in Example 1.

[0075] Comparative Example 4

[0076] The first additive is compound 1, the content of compound 1 is 5 wt %, the content of lithium difluorobis(oxaloyl)phosphate is 0.5 wt %, and the other steps are consistent with Example 1.

[0077] Comparative Example 5

[0078] No additives were added, and other steps remained the same as in Example 1.

[0079] Comparative Example 6

[0080] The first additive is compound 1, the content of compound 1 is 5 wt %, the content of lithium difluorobis(oxaloyl)phosphate is 5 wt %, and the other steps are consistent with Example 1.

[0081] In the present invention, Examples 1-10 and Comparative Examples 1-6 were used to prepare lithium-ion batteries using different electrolyte ratios, and the performance of the lithium-ion batteries was tested. The test results are shown in Table 1.

[0082] In one embodiment of the present invention, the low-temperature direct current resistance (DCR) test is to adjust the temperature of the thermostat to -20°C, let the lithium-ion battery stand in the thermostat for 2 hours, charge it at a constant current of 0.33C to 4.25V, then charge it at a constant voltage of 4.25V to 0.05C cutoff, let it stand for 30 minutes, and then discharge it at a constant current of 0.33C to 2.5V. Repeat the above charge and discharge cycle twice, and record the last discharge capacity as C0. After standing for 30 minutes, discharge it at 0.33C to 50% C0, adjust the state of charge (SOC) of the battery cell to 50%, let it stand for 30 minutes, record the static terminal voltage V1, discharge it at a constant current of C0 for 30 seconds, record the terminal voltage V2 and current I, and calculate DCR = (V1-V2) / I.

[0083] In one embodiment of the present invention, the high-temperature storage capacity recovery rate test is to charge the lithium-ion battery to 4.25V at a constant current of 0.33C at 25°C, and then charge it at a constant voltage to a current of 0.05C, let it stand for 30 minutes, repeat 2-3 times, and record the last discharge capacity C1 at 0.33C. Then, place the fully charged lithium-ion battery in a constant temperature box at 60°C for 30 days, cool the battery cell, adjust the temperature of the constant temperature box to 25°C, let it stand for 10 minutes, discharge it to 2.5V at a constant current of 0.33C, and then charge and discharge it at a rate of 0.33C. The voltage range of charge and discharge is 2.5V-4.25V. After 2 cycles, record the last discharge capacity C2. The capacity recovery rate of the lithium-ion battery stored at high temperature is calculated according to the following formula: Capacity recovery rate (%) = (C2 / C1) × 100%.

[0084] In one embodiment of the present invention, the gas production growth rate test is to fully charge the lithium-ion battery, store it in a constant temperature box at 60°C, test its volume every 7 days, and record and calculate its volume growth rate, which is the gas production growth rate.

[0085] Table 1. Performance test results of lithium-ion batteries in Examples 1-10 and Comparative Examples 1-6

[0086]

[0087] As shown in Table 1, it can be seen from the comparison of Examples 1-10 and Comparative Example 4 that when the first additive and the second additive are used together, the low-temperature performance and high-temperature performance of the lithium-ion battery can be improved, the gas production of the lithium-ion battery can be reduced, and the safety of the lithium-ion battery can be improved. It can be seen from the comparison of Examples 1-5 and Comparative Example 1 that by adding the second additive, the low-temperature DCR of the battery is effectively reduced, and as the content of the second additive increases, the low-temperature DCR of the lithium-ion battery shows a decreasing trend, indicating that the higher the content of the second additive, the better the low-temperature performance of the lithium-ion battery. The reason is that the second additive can induce the formation of a thin and uniform inorganic-rich interface film, increase the migration rate of lithium ions at the interface, and thus improve the low-temperature performance of the lithium-ion battery. The increase in the content of the second additive shows a trend of first increasing and then decreasing for the high-temperature storage capacity recovery rate, and the 56-day gas production growth rate gradually increases. The reason is that the inorganic components in the interface film increase with the increase in the content of the second additive, and the inorganic-rich interface film has poor thermodynamic stability at high temperatures. Comparing Example 2 with Comparative Examples 1, 2, and 5, it can be seen that if the content of the second additive is too low or zero, the low-temperature performance of the lithium-ion battery is significantly reduced. If the content of the second additive is greater than or equal to 5wt%, the inorganic components of the resulting interface film are too high, causing decomposition at high temperatures, exacerbating gassing in the lithium-ion battery. Therefore, the content of the second additive should be controlled within a range of 0.1wt% to 3wt%, with an optimal content of, for example, 0.5wt% to 1wt%.

[0088] As shown in Table 1, by comparing Examples 2 and 6-9, it can be seen that the addition of the first additive will further reduce the low-temperature DCR of the lithium-ion battery. The reason is that the first additive, as a highly polar substance, can enhance the solubility of LiODFP through intermolecular interactions, allowing it to better exert its low-temperature effect. Moreover, as the content of the first additive increases, the capacity recovery after 30 days of storage at 60°C first increases and then decreases, and the gas production growth rate after 56 days is optimized, indicating that there is an optimal content for the first additive. This is because the unsaturated bonds in the structure of the first additive can capture the F- generated by the PF bond breakage, forming a CF covalent bond, and further causing a chain addition reaction on the positive electrode side, thereby improving the stability of the positive electrode interface and thus improving the high-temperature performance. Excessive use of compound 1 will cause the CEI film to be too thick during high-temperature storage, which is not conducive to the performance of the lithium-ion battery capacity.

[0089] As shown in Table 1, it can be seen from Comparative Example 2 and Comparative Examples 3, 4 and 6 that if the content of the first additive is too low or 0, on the one hand, the first additive cannot assist LiODFP to better play a low-temperature role, and on the other hand, the high-temperature performance of the lithium ion battery is also greatly reduced. If the content of the first additive is too high, the molecules themselves are prone to excessive decomposition in the later storage stage of the lithium ion battery, which deteriorates the storage performance and gas production performance. Therefore, the content of the first additive needs to be controlled within a reasonable range, and the content of the first additive should be controlled within 0.1wt%-3wt%, and the optimal content is, for example, 0.5wt%-1wt%. As can be seen from Comparative Example 2 and Example 10, when the second additive is combined with the first additive with different structures, the content is controlled within a reasonable range, and the low-temperature effect of LiODFP can also be fully played, and the high-temperature storage and gas production performance are also possessed.

[0090] The application further provides an electronic device comprising at least one lithium ion battery as described above for providing electric energy. The electronic device can be a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy and an electric tool, etc. In an embodiment of the application, the vehicle is, for example, a new energy vehicle, which can be a pure electric vehicle, a hybrid vehicle or a range extended vehicle, etc. The spacecraft includes an airplane, a rocket, a space shuttle and a spacecraft, etc. The electric toy includes a fixed or mobile electric toy, such as a game console, an electric vehicle toy, an electric ship toy and an electric airplane toy, etc. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembling electric tool and a railway electric tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator and an electric planer, etc. The electronic device comprises the lithium ion battery as described above, and thus has the advantages of the lithium ion battery as described above, which will not be described herein.

[0091] In summary, the application provides a lithium ion battery electrolyte and its application. By using the first additive and the second additive together, the solubility of the second additive can be enhanced through intermolecular interaction. The unsaturated bond in the first additive can capture F- generated by the breaking of P-F bond to form a C-F covalent bond, further addition reaction of the chain occurs on the positive electrode side, the stability of the positive electrode interface is improved, the decomposition gas of the non-aqueous solvent is reduced, and the transition metal ions in the positive electrode are protected from HF corrosion. By using the first additive and the second additive together, the advantages of both can be fully utilized, the quality of the positive electrode-electrolyte interface and the negative electrode-electrolyte interface can be improved, the battery impedance can be effectively reduced, the low-temperature performance of the battery can be improved, and the high-temperature performance and gas production performance are also considered.

[0092] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by the specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept, such as the technical solutions formed by the mutual replacement of the above-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.

[0093] Except for the technical features described in the specification, the remaining technical features are known technologies to those skilled in the art. In order to highlight the innovative features of the present invention, the remaining technical features will not be described here in detail.

Claims

1. A lithium ion battery electrolyte, characterized in that At least the following components: non-aqueous solvents; lithium salts; as well as Additives, the additives comprising a first additive and a second additive, the first additive being selected from at least one of the following compounds: Compound 1 or Compound 2; The second additive includes lithium difluorobis(oxaloyl)phosphate; the content of the first additive in the electrolyte is 0.1wt%-3wt%, and the content of the second additive in the electrolyte is 0.1wt%-3wt%.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that The content of the first additive in the electrolyte is 0.5 wt%-1 wt%, and the content of the second additive in the electrolyte is 0.5 wt%-1 wt%.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that The non-aqueous solvent is selected from at least one of ethylene carbonate, polycarbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, propyl propionate, ethyl propionate or ethyl acetate, and the content of the non-aqueous solvent in the electrolyte is 70wt%-85wt%.

4. The lithium-ion battery electrolyte according to claim 1, characterized in that The lithium salt is selected from one or a combination of at least two of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium methanesulfonate and lithium trifluoromethylsulfonate, and the content of the lithium salt in the electrolyte is 12 wt %-16 wt %.

5. A lithium-ion battery, characterized in that: The lithium-ion battery electrolyte comprises the electrolyte of any one of claims 1 to 4.

6. The lithium-ion battery according to claim 5, characterized in that The positive electrode active material of the lithium-ion battery includes Li x [Ni y Co z Mn t M (1-y-z-t) O 2-δ or at least one of lithium iron phosphate, wherein M is at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W or Zn, 0.9 < x < 1.1, 0 < y < 1.0, 0 < z < 1, 0 < t < 1, 0 ≤ δ ≤ 0.1; the negative electrode active material of the lithium-ion battery includes at least one of graphite, silicon oxide material or silicon carbon material.

7. An electronic device, characterized in that: A lithium-ion battery comprising the lithium-ion battery according to any one of claims 5 to 6.

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